Statement of the Technical Field
This document relates to compact antenna system structures, and more particularly, to a compact deployable antenna reflector structure.
Description of the Related Art
Various conventional antenna structures exist that include a reflector for directing energy into a desired pattern. One such conventional antenna structure is a radial rib reflector design comprising a plurality of reflector ribs joined together at a common cylindrical shaped hub. The reflector ribs provide structural support to a flexible antenna reflector surface attached thereto. A plurality of cords, wires, guidelines, or other tensile members couple the flexible antenna reflector surface to the reflector ribs. The wires or guidelines define and maintain the shape of the flexible antenna reflector surface. The radial rib reflector is collapsible so that it can be transitioned from a deployed position to a stowed position. In the deployed position, the radial rib reflector has a generally parabolic shape. In the stowed position, the reflector ribs are folded up against each other. As a result, the antenna reflector has a stowed height approximately equal to the reflector's radius.
Another conventional antenna structure is a folding rib reflector having a similar design to the radial rib reflector design described above. However, the reflector ribs include a first rib tube and second rib tube joined together by a common joint. In the stowed position, the first rib tubes are folded up against the second rib tubes. As such, the antenna reflector has a stowed height that is approximately half the stowed height of the radial rib reflector design. However, the stowed diameter of the folding rib reflector may be larger than the stowed diameter of the radial rib reflector design.
Another type of configuration is a hoop reflector where the reflector surface is attached to a circular hoop. In a hoop-type reflector, the hoop structure must have a certain amount of stiffness to prevent the hoop from warping. Typical of this design is U.S. Pat. No. 5,680,145. In this patent, the hoop consists of two rings, an upper and a lower. Both rings are made up of tube elements. As such, the single tube elements provide minimal bending stiffness, or ring stiffness, about the longitudinal axis of symmetry defined as the direction perpendicular to the circle defining the perimeter of the hoop. The limited ring stiffness allows the hoop to become non-circular and is easily deformed into an oval shape. Other hoop designs provide significant ring stiffness by creating a toroidal hoop with a triangular configuration of members. For example, such an arrangement is disclosed in U.S. Pat. No. 6,313,811. To shape the reflector into a parabolic surface, the hoop must also have a deployed thickness perpendicular to the plane defined by the perimeter of the hoop. The thickness of the hoop is measured in the direction of a central axis of the hoop when deployed. Moreover, this thickness must generally be greater than the depth of the parabolic surface in order to achieve a desired parabolic shape. The required out of plane thickness of the hoop and the need for bending stiffness can make it challenging to design a hoop structure which, when stowed, is sufficiently compact in length along the longitudinal direction defined by the hoop central axis. For example, a conventional hoop system having a sufficiently rigid hoop structure with a deployed thickness H can, when collapsed for stowage aboard a spacecraft, have an elongated length along the hoop center axis equal to 2H.